Machines used to spread granular fertilizer on the soil are trailer-type vehicles having hoppers for carrying the material. An endless conveyor is driven to deliver the material from the bottom of the hopper onto spreading discs. Examples of these machines are shown by Tyler in U.S. Pat. Nos. 3,450,431 and 3,539,133. The conveyors and discs of these machines are driven through a power takeoff structure attached to the towing vehicle. The ground supporting wheels for the machines are not used to drive the conveyor and spreading discs. Some fertilizer spreaders have driven wheels located in frictional engagement with the ground engaging wheels to transmit power from the ground engaging wheels to the spreader disc drive structure. This type of drive is shown in U.S. Pat. Nos. 3,085,807 and 3,220,740. When this drive is used in wet or muddy conditions, there is substantial slippage between the ground engaging wheel and the driven wheel which results in a loss of power and inefficient operation of the material spreading discs. Another ground wheel drive arrangement having a clutch and chain and sprocket drive for operating spreading discs of a fertilizer spreader is disclosed in U.S. Pat. No. 3,184,243.